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[SEDONA-479] Update RS_Normalize #1232

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Feb 4, 2024
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[SEDONA-479] Update RS_Normalize #1232

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19 changes: 12 additions & 7 deletions common/src/main/java/org/apache/sedona/common/raster/MapAlgebra.java
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Original file line number Diff line number Diff line change
Expand Up @@ -423,18 +423,23 @@ public static double[] logicalOver(double[] band1, double[] band2) {
}

/**
* @param band band values
* @param bandValues band values
* @return an array with normalized band values to be within [0 - 255] range
*/
public static double[] normalize(double[] band) {
double[] result = new double[band.length];
double normalizer = Arrays.stream(band).max().getAsDouble() / 255d;
public static double[] normalize(double[] bandValues) {
Double minValue = Arrays.stream(bandValues).min().orElse(Double.NaN);
Double maxValue = Arrays.stream(bandValues).max().orElse(Double.NaN);

for (int i = 0; i < band.length; i++) {
result[i] = (int) (band[i] / normalizer);
if (Double.compare(maxValue, minValue) == 0) {
// Set default value for constant bands to 0
Arrays.fill(bandValues, 0);
} else {
for (int i = 0; i < bandValues.length; i++) {
bandValues[i] = ((bandValues[i] - minValue) * 255) / (maxValue - minValue);
}
}

return result;
return bandValues;
}

/**
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18 changes: 14 additions & 4 deletions common/src/test/java/org/apache/sedona/common/raster/MapAlgebraTest.java
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Expand Up @@ -315,10 +315,20 @@ public void testLogicalOver() {

@Test
public void testNormalize() {
double[] band = new double[] {800.0, 900.0, 0.0, 255.0};
double[] actual = MapAlgebra.normalize(band);
double[] expected = new double[] {226.0, 255.0, 0.0, 72.0};
assertArrayEquals(expected, actual, 0.1d);
double[] band1 = {800.0, 900.0, 0.0, 255.0};
double[] band2 = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
double[] band3 = {16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31};
double[] band4 = {-16,-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1};
double[] actual1 = MapAlgebra.normalize(band1);
double[] actual2 = MapAlgebra.normalize(band2);
double[] actual3 = MapAlgebra.normalize(band3);
double[] actual4 = MapAlgebra.normalize(band4);
double[] expected1 = {226.66666666666666, 255.0, 0.0, 72.25};
double[] expected2 = {0.0, 17.0, 34.0, 51.0, 68.0, 85.0, 102.0, 119.0, 136.0, 153.0, 170.0, 187.0, 204.0, 221.0, 238.0, 255.0};
assertArrayEquals(expected1, actual1, 0.1d);
assertArrayEquals(expected2, actual2, 0.1d);
assertArrayEquals(expected2, actual3, 0.1d);
assertArrayEquals(expected2, actual4, 0.1d);
}

@Test
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2 changes: 1 addition & 1 deletion docs/api/sql/Raster-operators.md
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Expand Up @@ -2468,7 +2468,7 @@ This function only accepts integer as factor before `v1.5.0`.

### RS_Normalize

Introduction: Normalize the value in the array to [0, 255]
Introduction: Normalize the value in the array to [0, 255]. Uniform arrays are set to 0 after normalization.
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What do you mean by this?

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@prantogg prantogg Feb 2, 2024 •
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Arrays with all identical values are set to 0 after normalizing


Format: `RS_Normalize (Band: ARRAY[Double])`

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